I think the USMCA may complicate the tariffs on Canada and Mexico. This trade agreement likely has some specific details on what can and cannot be done with Tariffs. The reason the Fentanyl Emergency was used for justification is likely a carve-out in the USMCA to apply additional tariffs.

We don't have a USMCA with all these other countries so it is probably easier to just say we're going to charge you half the tariff you charge us and we reserve the right to raise them further. There is a baseline 10% for all countries, because it appears all countries charge the US at least 10% and that is a matching tariff.